In multi-component structures such as those that comprise energy generation and storage devices such as batteries, supercapacitors, fuel cells, solar cells, and the like, components with defects or abnormal features or flaws can adversely affect the properties of the assembled device. As a result, the performance and service life of such devices can be significantly reduced (for example, by degraded capacity). Such defective devices often fail prematurely. Quality control of battery components is especially important since these devices are increasingly used to power expensive mission critical equipment.
Holographic interferometry is a method of reconstructing to a very high precision the original waveform of light emitted or reflected by an object. This method allows image resolution close to that of the wavelength of the light being used. The non-destructive method of holographic interferometry coupled with impulse heating of the test article to allow observation of its dynamic response to operating conditions, as described below, is the one of most effective non-contact automated quality control methods available.
To perform holographic interferometry, the most common technique is to allow coherent light (such as laser light) to fall on an object. The reflected light is then combined with a reference beam of the original light to produce an interference pattern that projected onto a piece of film, or recorded by a CCD (charge-coupled device) and read into a computer. By passing a beam of the same wavelength as the beam used to record the hologram, the image thus obtained may be re-projected.
Holographic interferometry was first used to study fluid flow around objects of varying profiles (see Tim McIntyre's introduction). After passing the laser beam through a splitter, one beam of the laser light is passed through the flow to be studied, and the other beam is diverted around the flow chamber. The two beams are then re-combined in the manner described above; producing an interference pattern from which the forms of the fluid flow may be reconstructed.
The method has several advantages, one of these being that it can determine the response of a device to the kinds of changes in environmental or operating conditions that can indicate flaws or defects that may not be apparent in more standardized tests. For example, and as described below as an advantage of the present invention, the method of holographic interferometry can precisely determine the physical response of battery electrodes to small temperature changes. Such a response can indicate whether the battery electrode is properly formed and installed into the battery.